1. Field of the Invention
Exemplary aspects of the present invention relate to a fixing device, and more particularly to a fixing device including a fixing member, a pressure member, and a temperature detection mechanism to fix a toner image on a recording medium. In addition, the present invention also relates to an image forming apparatus including the fixing device.
2. Description of the Related Art
Image forming apparatuses such as printers, copiers, facsimiles, and multifunctional peripherals capable of serving at least two functions of printer, copier and facsimile have been demanded to reduce the start-up time thereof. Specifically, a fixing device of the image forming apparatus is expected to have reduced the start-up time thereof to meet such demand.
In one example, an attempt is made to reduce the start-up time of a fixing device fixing a toner image on a recording medium by disposing a heating roller acting as a fixing member and a support roller acting as a pressure member. The heating roller includes a cylindrical support member and a resistance-heating layer having a self-temperature-control property. Since the resistance-heating layer is formed along an outer circumference of the cylindrical support member to heat the heating roller, a surface of the heating roller can be easily heated, thereby reducing the start-up time of the fixing device.
Another example attempts to reduce the prolongation of the start-up time of a fixing device employing a fixing belt by disposing a heat source outside a fixing roller. A surface of the fixing roller is covered with an elastic member. Since the heat source is not internally disposed in the fixing roller, the prolongation of the start-up time can be reduced even when the elastic layer increases a thickness thereof.
A related-art fixing device including the above-mentioned examples includes a fixing member and a pressure member. In the course of a fixing process, for example, the fixing member is heated and is pressed against the pressure member to form a nip therebetween. When the recording medium passes through the nip, the toner image carried thereon is fused, thereby fixing the toner image thereon.
In such a related-art fixing device, the fixing member is heated during the start-up time. When a surface of the fixing member reaches an appropriate temperature for the fixing process, the recording medium is conveyed into the nip between the fixing member and the pressure member, thereby fixing the toner image thereon.
For example, when a plurality of recording media successively pass through the nip, an interval is generated between a tailing end of a precedent recording medium and a leading end of a following recording medium. Specifically, the interval is generated between a time at which the tailing end of the precedent recording medium is conveyed out from the nip and a time at which the leading end of the following recording medium is conveyed into the nip. The fixing member and the pressure member contact each other without having the recording medium therebetween during the interval. Consequently, an amount of heat is transferred from the fixing member to the pressure member when the temperature of the pressure member is lower than a certain temperature. For example, the temperature of the pressure member is often lower than the certain temperature shortly after the completion of the start-up time of the fixing member. In this regard, when the fixing member has a relatively low heat capacity, the temperature thereof decreases due to the transfer of the heat therefrom to the pressure member. This heat transfer can cause a decrease in the surface temperature of the fixing member to below the appropriate temperature for the fixing process, resulting in the fixing error of the toner image on the recording medium.
Therefore, a fixing member having a relatively high heat capacity is employed to reduce such a problem. However, such a fixing member needs a longer time period to increase the surface temperature thereof to an appropriate temperature for the fixing process during the start-up, resulting in a longer waiting time for a user.